The invention relates to a system for energy conversion from a flow of fluid into transportable energy, comprising a fluid driven device connected to a tether wherein the tether is coupled with a base station.
Energy demand for human consumption has significantly increased over the last decades and it has been forecasted that, due to growth of the world population, energy demand will further grow. Energy, according to the definition of physicists, can neither be created nor consumed or destroyed. However, energy may be converted or transferred to different forms. These forms can be, for example mechanical or electrical energy. At present a significant portion of the supplied mechanical and electrical energy is based on energy conversion by means of combustion of fossil fuels. These fossil fuels have been developed in billions of years and it has been predicted that mankind is utilizing them in a period of a few hundred years. Besides the problem that we will run out of fossil fuels at a certain moment, investigations show that combustion of fossil fuels contributes significantly to air pollution and the production of greenhouse gas. Due to the production of greenhouse gasses it has been projected that the Earth's surface temperature could exceed historical analogs affecting most ecosystems on Earth.
As a way forwards, it is proposed to save these valuable fossil resources for purposes that fully rely on fossil fuels and that alternative forms of energy, preferable renewables such as wind, sun and tidal energy are being used for purposes that have a less direct demand for fossil fuels such as, for example, production of electricity.
Even though renewable energy has been recognized as a resource for global energy demand, due to the nature of renewable energy, there are a number of issues to tackle. One of them is that the amount of energy available is restricted. Furthermore the number of locations available for harvesting renewable energy is limited. From this it can be concluded that if renewable energy has to make a significant contribution to the worlds energy demand, the need is brought forward to convert renewable energy at available locations with the highest possible conversion rate. An additional challenge is that the price of renewable energy has to be at such a level that a transition from conventional energy to renewable energy can be borne by the market. This brings forward the additional requirement that conversion has to be cost-effective.
Humans have converted energy from a flow of fluid, for example wind or moving water, since mankind. Energy conversion from moving water has many similarities to energy conversion from wind. However, differences are that, the density of water is about one thousand times greater than the density of air, and in general the velocities of moving water are less than those of wind, and water streams, such as tidal and Gulf streams, are more predictable than those of wind. Further differences are found in the velocity profiles of wind and water streams. For example, it is known that the flow of fluid of tidal currents is not homogenous and that the flow is a complex interaction of several processes. Wave-induced eddies at the sea surface and eddies created by the seabed have a significant effect on the velocity profile of tidal currents causing practical problems for converting energy from these types of moving water bodies.
US2002/004090948A1 Apr. 11, 2002 by inventor Gary Dean Ragner discloses a conversion system wherein multiple airfoil kites in tandem are attached by means of control lines and support lines to a control housing. The control lines can change length to control the airfoils kites' angle-of-attack, pitch angle, direction of flight, and flight speed. The length of control lines are controlled from ground station to adjust the airfoils' direction to follow a specific flight path. Control lines and support lines are also wound on a power shaft in control housing. The control of this known system is complex and due to the long control cables the system is difficult to control. Due to the requirement to reel them in and out the cables are subjected to extensive tear and wear which is introducing frequently inspection and maintenance activities. Furthermore, due to the inability of this known system to make short radius turns, the system is operated with a digit eight or an oval shaped trajectory resulting in a large energy leakage. Also, due to controlling the airfoil kites in tandem, it is not possible to adjust the angle-of-attack of each airfoil kite individually. This is disadvantageous as, due to the long string of kites, the apparent direction of flow experienced by the individual kites is different to each other.
Besides that next to the aforementioned system other types of systems are known that are able to convert energy, all the known systems suffer from a number of disadvantages:    a) The known systems have a low conversion rate and as a result the majority of the available energy remains untouched. At present, the common way of mitigating these disadvantages is to install multiple systems in series. The function of the systems installed downstream of the first system is merely to compensate for the weak performance of the first system. It goes without saying that the cost of developing such a row of systems is much higher than the installation of a single system that is able to convert the available energy in one go.    b) The known systems suffer furthermore from a low efficiency caused by significant losses during conversion and transfer of the converted energy. As the converted energy most of the time is consumed at a remote location, the losses during transfer of energy have a significant impact on the system performance.    c) Components used in the known systems are subjected to extensive tear and wear and/or the systems have been designed such that inspection and maintenance is complex and expensive.